Synergistic ep additive: a mixture of mercaptobenzothiazole and an arylidene amine



United rates SYNERGISTIC EP ADDITIVE: A MIXTURE OF M'ER'CAPTOBENZOTHIAZOLE AND AN ARYLIDENE AMINE No Drawing. Application December 16, 1954, Serial No. 475,825

Claims. (Cl. 252-475) This invention relates to a synergistic EP mixture of compounds for lubricating oils. More particularly, this invention involves a discovery that a mixture of a mercaptobenzothiazole and a Schifis base reaction product possesses a synergistic EP action in both hydrocarbon and synthetic oleaginous lubricating oils.

The extreme pressure additive combination of this invention comprises a mixture of a mercaptobenzothiazole or an aliphatic nuclear-substituted derivative thereof and a Schiffs base reaction product having the general formula ACH=NRN=CH-A, wherein A is an aromatic nucleus and R is an aliphatic radical having two N atoms directly attached to difierent carbon atoms of the same open chain. The concentration of the EP additive mixture is within the range of 0.05 to 1.5% by weight of the lubricant composition and the mol ratio of mercaptobenzothiazole to Schifis base reaction produce is between 0.5:1.0 and 4:1.

The increasing speeds and torques available in modern automotive equipment have caused increased bearing pressures and rigorous service conditions on the gear teeth of hypoid gears and on other instances of metal to metal contact. As a consequence, the extreme pressure requirements of lubricants have steadily risen and it has been necessary to incorporate extreme pressure agents in a great number of greases and lubricating oils. The most effective extreme pressure agents known prior to the instant invention were of the active sulfur, active halogen or combined active sulfurhalogen type. Active sulfur extreme pressure compounds are exemplified by sulfurized fatty acids and organic disulfides; an example of an active chlorine agent is chlorinated parafiin wax; combined active sulfur-chlorine agents are exemplified by sulfochlorinated sperm oil. These extreme pressure agents which require a concentration of about 3 to 15 per cent of the total lubricant composition in order to be effective have the disadvantage that they tend to be corrosive and require the presence or" oil-soluble corrosion inhibitors.

The synergistic EP additive of this invention is effective in very small concentrations. The elfectiveness of the additive mixture in concentrations between 0.05 and 1.5 weight per cent is a substantial advantage over E? agents of the prior art which usually are employed in the concentration range between 3 and 15 weight per cent of the total composition.

Another advantage resides in the fact that the EP additive mixture of this invention is not corrosive. As a matter of fact, it is an excellent anti-corrosive agent and the individual components, namely, the mercaptobenzothiazole and the Schifis base reaction product are wellknown additives which are sold as anti-corrosive agents.

Mercaptobenzothiazole has the following structural formula:

o-srr ice In its aliphatic-substituted derivatives, one or more of the hydrogen atoms on the benzo radical are replaced by aliphatic hydrocarbon radicals. Examples of aliphatic hydrocarbon-substituted mercaptobenzothiazoles, which combine with a Schitfs base reaction product to form an outstanding synergistic EP additive, are as follows: 4 ethyl-mercaptobenzothiazole, 5 methyl-mercaptobenzothiazole, -heptyl-mercaptobenzothiazole, 5-(1-propenyl)-mercaptobenzothiazole, 4-lauryl-mercaptobenzothia zole, and 4-(n-2-butenyl)-mercaptobenzothiazole. The aliphatic radical advantageously contains 1 to 12 carbon atoms, but mercaptobenzothiazoles substituted on the benzo nucleus with higher alkyl and alkenyl radicals can also be employed.

The second component of the synergistic EP additive mixture of this invention is a Schifis base reaction product of one mol of an aliphatic polyamine having two primary amino groups with 2 mols of an aromatic aldehyde, said Schiifs base reaction product having the formula ACH=NRN=CHA, where A represents an aromatic nucleus, and R represents an aliphatic radical having two nitrogen atoms attached directly to difierent carbon atoms of the same open chain. Compounds of this type have previously been disclosed as metal deactivators in Dowing et al. No. 2,282,513. However, it was entirely unexpected that such Schiifs base reaction products in combination with mercaptobenzothiazole forms an excellent EP additive. Any of the various arylidene amines disclosed in said patent may be employed for purposes of the present invention.

By way of example, the following compounds of this class are listed as being suitable for purposes of the pres ent invention:

Di-(2-hydroxy-3-methoxybenzal) ethylenediamine Di-(Z-hydroxybenzal) ethylenediamine Di-(Z-hydroxybenzal) decamethylenediamine Di-(Z-hydroxybenzal) triethylenetetramine Di-(2-hydroxybenzal) hexamethylenediamine Di-(Z-hydroxybenzal) 1:3 propylenediamine Dibcnzal ethylediaminev Dibenzal hexamethylenediamine Dibenzal diethylenetriamine Dibenzal triethylenetetramine Disalicylal ethylenediamine As representative of a preferred compound of this class which is commercially available, there may be mentioned disalicylal propylene diamine, which is also known as di-salicylidene-1,2-diaminopropane. This is sold under the trade name DMD by E. I. du Pont de N'emours and Company and by Tennessee Eastman as Tenamene 60.

The mercaptobenzothiazole component usually constitutes the major portion of the EP additive mixture, and the preferred ratio of mercaptobenzothiazole to Schifis reaction product is in the range of 1.5:1 to 3:1. However, the EP additive mixture can contain a mol ratio of mercaptobenzothiazole to Schifis base reaction product between 0.5 :1 and 4:1.

The EP additive mixture usually constitutes 0.5 to 1.0 weight per cent of the total lubricant composition. However, as has been pointed out previously, significant improvement in EP properties is obtained with a weight percentage of additive as low as 0.05. The upper limit of EP additive mixture concentration is usually set at about 1.5 weight per cent, since higher concentrations do not show any advantage over the prescribed concentration range.

The EP additive mixture of this invention imparts exceptional extreme pressure properties to both grease and lube oil compositions. In general, the concentration of the additive mixture is in the upper portion of the specified 0. to 1.5 weight per cent range in grease composition, whereas in the lower portion of this range when employed in lube oil compositions.

The oleaginous lubricating base can be a hydrocarbon mineral oil, a synthetic lubricating base or mixtures thereof. If a hydrocarbon mineral oil is the base, it is either a paraflin base or a napthene base fraction which advantageously has undergone solvent refining to .improve its lubricity and its viscosity-temperature relationships. For certain applications such as greases, straight vacuum distillate lube fractions that have not undergone extensive solvent refining are employed as the lubricating base in which the EP mixture of the invention is incorporated. In general, it can he stated that wide variety of lube oil fractions are contemplated for use in the lubricating compositions of this invention; for example, parafiin base and napthene base lube oil fractions having an SUS viscosity at 100 F. between 50 and 5,000 may be used as the base oil in the compositions of this invention.

The EP additive mixture of this invention is particularly efiective in synthetic oleaginous lubricating bases. These bases which normally form the major portion of the lubricating medium comprise aliphatic dicarboxylic acid esters, polyesters, hydrocarbon-soluble polyalkylene others, tetra hydrocarbon-substituted silicates and the sulfur derivatives thereof. Although any one of these types of synthetic lubricating compounds can be used, the aliphatic dicarboxylic acid esters are preferred. Compounds wi-thin this particular class are the esters of such acids as sebacic, adipic, pimelic, azelaic, alltenylsuccinic, alkylmaleic, etc. The esters thereof are preferably the aliphatic esters and particularly the branched chain alip'hatic diesters. Specific examples of the preferred oleaginous compounds are di-2-ethylhexyl sebacate, di-2-ethyl hexyl azelate, di-Z-ethylhexyl adipate, di-sec-amyl sebacate, di-Z-ethylhexyl alkenylsuccinate, di-Z-ethoxyethyl sebacate, di-Z-(Z'methoxyethoxy)ethyl sebacate, di-2- (2'-ethy-lbutoxy) ethyl sehacate, di-Z-butoxyethyl azelate, di-2-(2'-butoxyethoxy) ethyl alkenylsuccinate, etc.

In addition to the aliphatic dicarboxylic acid esters described above, polyester lubricants formed by a reaction of an aliphatic dicarboxylic acid, a glycol and a monofunctional compound, which is either an aliphatic monohydroxy alcohol or an aliphatic monocarboxylic acid, in specified mol ratios are also employed as the synthetic lubricating base in the compositions of this invention; polyesters of this type are described in U. S. 2,628,974. Polyesters formed by reaction of a mixture containing specified amounts of 2-ethy-l-l, 3'hexanediol, sebacic acid and 2-ethylhexanol and by reaction of a mixture containing adipic acid, diethylene glycol and 2-ethylhexanoic acid illustrate this class of synthetic polyester lubricating bases.

Water-insoluble polyalkylene ethers as illustrated by polyglycols are also used as a synthetic lubricating base in the compositions of this invention. Polypropylene glycol, polybutylene glycols and mixed polyethylene-polypropylene glycols are examples of this class of synthetic lubricating bases.

'The sulfur analogs of the above-described diesters, polyesters and polyalkylene ethers are also used in the formulation of the lubricating compositions of this invention. Dithioesters are exemplified by di-Z-ethylhexyl thiosebacate .and di-n-octyl thioadipate; polyethylene thieglycol is an example of the sulfur analogs of the polyalkylene glycols; sulfur analogs of polyesters are exemplified by the reaction product of adipic acid, thioglycol and Z-ethylhexyl mercaptan.

Tetra-hydrocarbon-substituted silicates having a general formula.

wherein R, R' ,.R", and R' are similar-or dissimilar bydrocar'bon radicals may also be used as a part of the oleaginous lubricating base. Tetra-aliphatic esters such as tetra-octyl silicate, tetra-lauryl silicate, tetra-amyl silicate and tetra-decyl silicate are preferred silicate esters but aryl esters such as tetraphenyl silicate and cycloaliphatic silicates such as tetra-cyclohexyl silicates may also be used.

The synergistic extreme pressure properties of the additive combination of this invention were demonstrated by the following tests:

Mean Hertz load test SAE-SOD test One-hour wear test The one-hour Wear test is also run on the Shell fourball machine, and is eifected under the following conditions:

Duration 1 hour at each load. Test temperature No heat control. Oil charge 15cc.

Speed 1,800 R. P. M.

The balls, first grade SKF steel, are cleaned with Stoddard Solvent and MEK, then dried; the lower balls are locked in position and a fresh 10 to 15 cc. charge of test oil is poured into the test cup. A one-hour run at 1,800 R. P. M. 140 ft. per min, is made at l and 10 kg. loads. The scar diameters of the three lower balls are measured horizontally and vertically and the average of the six readings is taken. From this, the conversion of scar diameter in millimeters is obtained. The torque counter readings are taken at the endof l, 10, 30 and 60 minutes.

The SAESOD test is described on page 9 of a report entitled Synthetic Lubricants by \V. E. Turk, of Standard Oi-l Development Company, issued by Wright Air Development Center in October 1953. The final value is the average of three runs which are made under the following test conditions:

Main shaft speed"- 1,000 R. P. M.

Shaft speed ratio 3.5/1.

Test cups Timken T-48651.

Run-in schedule 50 lb. for 2 min. (used at Beacon).

Loading after run-in. Manual, step-wise, 50 lb. at 10 sec.

intervals.

Failure load Minimum load at which scu'ffing of test cups occurs.

The mean Hertz load test is described in U. S. 2,600,058.

The synergistic action of the EP additive of this invention was demonstrated in a base oil comprising 81.5

per cent di-Z-ethylhexyl azelate, 18 per cent of a commercial V. .I. improver comprising about 40% by weight.

of butyl methacrylate polymer in di-Z-ethylhexyl sebacate as a carrieroil, and 0.5 per cent phenothiazine which acts as a corrosion inhibitor. In the following tables there are shown the results of adding mercaptobenzothiazoleand an arylidene amine separately, and of adding a mixture of these two reagents on the EP properties .of this base oil. In the following tables MBT denotes mercaptobenzothiazole and DDP identifies a concentrate comprising per cent disalicylidene 1,2-diaminopropane and 20 per cent toluene.

In Table 'I, the synergistic EP properties .of the mixtures mentioned were demonstrated in the mean Hertz load test.

In Table II, the synergistic EP properties of a mixture of a mercaptobenzothiazole and an arylidene amine were demonstrated in the SAE-SOD Test.

In Table III, the synergistic EP additive of the invention was shown to possess synergistic EP properties in the one-hour wear test.

Table III One-hour wear 1 kg. 10 kg.

Base 011 406 .615 Base oil+0.2% DDP 368 660 Base 0il+0.4% MBT 236 279 Base 0il+0.2% DDP and 0.4% MBT 165 231 The addition of 0.2 Weight per cent DDP and 0.4 weight per cent MBT to the base oil resulted in a lubricating composition which passed the seizure-weld test which is run on the Shell four-ball machine and is included in Government Specification MIL-L-7808.

The data in the foregoing tables clearly demonstrate the synergistic EP action of mixtures of mercaptobenzothiazole and an arylidene amine in a synthetic base oil. Although all of the data is obtained in a synthetic base oil consisting predominantly of an aliphatic dicarboxylic ester, similar results are obtained when a mixture of mercaptobenzothiazole and arylidene amine are incorporated in hydrocarbon base oils or a base oil comprising a mixture of hydrocarbon and synthetic base oil.

Aliphatic derivatives of mercaptobenzothiazole are combined with arylidene amines of the prescribed type to form synergistic EP additives. Moreover, other arylidene amines such as dibenzal ethylenediamine, disalicylal ethylenediamine, and di-(Z-hydroxybenzal) ethylenediamine form synergistic EP additives with mercaptobenzothiazole and aliphatic-substituted derivatives thereof.

Obviously, many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and, therefore, only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A lubricant composition consisting essentially of an oleaginous liquid containing a corrosion inhibiting amount of phenothiazine and 0.051.5% by weight of a mixture in a 1:2-4:1 mol ratio of a compound selected from the class consisting of mercaptobenzothiazole and its homologs containing at least one aliphatic hydrocarbon radical substituted on the benzol nucleus and a disalicylal alkylene diamine wherein the alkylene group is a Cz-e alkylene group and the amine groups are attached to different carbon atoms thereof.

2. Claim 1 wherein said mixture consists of mercaptobenzothiazole and disalicylal propylene diamine.

3. Claim 1 wherein the said oleaginous liquid comprises in major proportion at least a dicarboxylic acid ester.

4. A lubricating composition consisting essentially of an oleaginous liquid comprising at least in major proportion a dicarboxylic acid ester and containing a corrosion inhibiting amount of phenothiazine and 0.05-1.5% by weight of a mixture in a 1:2-4zl mol ratio of mercaptobenzothiazole and disalicylal propylene diamine.

5. Claim 4 wherein the mercaptobenzothiazole and disalicylal propylene diamine are in a mol ratio of 2:1.

References Cited in the file of this patent UNITED STATES PATENTS 2,201,258 Busse May 21, 1940 2,282,513 Downing et al. May 12, 1942 2,382,906 Pederson et al. Aug. 14, 1945 FOREIGN PATENTS 488,390 Great Britain July 6, 1938 

1. A LUBRICANT COMPOSITIN CONSISTING ESSENTIALLY OF AN OLEAGINOUS LIQUID CONTAINING A CORROSION INHIBITING AMOUNT OF PHENOTHIAZINE AND 0.05-1.5% BY WEIGHT OF A MIXTURE IN A 1:2-4:1 MOL RATIO OF A COMPOUND SELECTED FROM THE CLASS CONSISTING OF MERCAPTOBENZOTHIAZOLE AND ITS HOMOLOGS CONTAINING AT LEAST ONE ALIPHATIC HYDROCARBON RADICAL SUBSTITUTED ON THE BENZL NUCLEUS AND A DISALICYLAL ALKYLENE DIAMINE WHEREIN THE ALKYLENE GROUP IS A C2-6 ALKYLENE GROUP AND THE AMINE GROUPS ARE ATTACHED TO DIFFERENT CARBON ATOMS THEREOF. 